Field of the Invention
The present invention relates to a sample observation device and a sample observation method.
Description of the Related Art
As a method for observing a colorless and transparent sample, modulation contrast method is available. In an observation device using the modulation contrast method, an aperture plate is disposed at the illumination optical system, and a modulator is disposed at the observation optical system. Here, the aperture plate is conjugate to the modulator. Moreover, at the aperture plate, a rectangular transmission part is formed at a position away from the optical axis (the center of the aperture plate). Meanwhile, at the modulator, a plurality of regions having mutually different transmittance is formed. These regions are formed to be adjacent to each other. These regions each have a dimension (width) capable of including an image of the transmission part.
As stated above, the transmission part is formed at a position away from the optical axis. Therefore, illumination light passing through the transmission part is emitted from a condenser lens so as to illuminate a sample from an oblique direction. The illumination light emitted from the condenser lens passes through the sample and reaches the modulator. Here, three regions of region A (transmittance 100%), region B (transmittance 20%) and region C (transmittance 0%) are formed at the modulator, for example.
In the case where a surface of the sample is flat, a light flux passing through the sample reaches the region B of the modulator. As a result, a sample image having brightness corresponding to the transmittance of the region B is formed. When the sample surface is an inclined face that is an upward-slope to the right, the light flux is refracted to the right at the time of passing through the sample. In this case, the light flux passing through the sample reaches the region C of the modulator. As a result, a sample image having brightness corresponding to the transmittance of the region C is formed. When the sample surface is an inclined face that is an upward-slope to the left, the light flux is refracted to the left at the time of passing through the sample. In this case, the light flux passing through the sample reaches the region A of the modulator. As a result, a sample image having brightness corresponding to the transmittance of the region A is formed. As just described, when the sample is colorless and transparent, and has a flat face and an inclined face, then the flat face part in the sample image appears gray, and the inclined face part appears black or white.
As just described, in the modulation contrast method, it is possible to observe a colorless and transparent sample as well as an image that has a shadow (contrast) and gives a three-dimensional appearance. As observation devices using the modulation contrast method, observation devices described in Japanese Patent Application Laid-Open No. Sho 51-29149 and Japanese Patent Application Laid-Open No. 2004-126590 are available.